This week, Dr. Sydney Spiesel discusses whether sex late in pregnancy makes women go into labor, the link for kids between being overweight and getting too little sleep, and the risk of serious blood clots during air travel.
Question: Does sex late in pregnancy set off labor? A lot of folklore says it does and, for that reason, some obstetricians warn their patients against it. There are good scientific arguments to make us expect that the idea might be true. For instance, prostaglandin E., an ingredient of semen, stimulates uterine contraction and can start labor. So can breast stimulation, and orgasm while having sex during pregnancy increases uterine activity.
Context: Actually, it would be very desirable if sex did play this role. For sound medical reasons—usually to protect the fetus from the negative effects of more than 42 weeks gestation or from the problems associated with maternal diabetes—doctors now use artificial means to stimulate the onset of labor. The artificial methods are amniotomy ("breaking of the waters") and medications that stimulate contractions. But there are certain disadvantages: a higher rate of cesarean sections, forceps-assisted delivery, bleeding after delivery, and prolonged labor. In addition, by several different measures, the babies on average don't do quite as well.
New study: If having sex late in pregnancy proved to be an effective natural method of starting off labor, it might be superior to the artificial methods (and many women might prefer it). Three obstetricians at the University of Malaysia set out to explore this question by recruiting a group of about 200 women late in pregnancy, chosen because they were all scheduled to be induced within the week if they didn't spontaneously go into labor. Half the women were actively encouraged to have vaginal sex, and the remaining half—the control group—were neither encouraged nor discouraged.
Findings: About 60 percent of the women encouraged to have sex did so, compared with only 40 percent of the control group. So, did this increased rate of rowdiness trigger more spontaneous labor? Nope. The rate was virtually the same in both groups, as was the likelihood of complications like maternal fever, cesarean section, excess bleeding, or evidence of increased newborn stress or other problems.
Conclusion: Given these findings, then, there is no particular reason to recommend sex late in pregnancy as a way of averting artificial induction of labor. But the study suggests that there is a different benefit: pleasure. Of the women in both groups who reported having sex in the last week of pregnancy, more than 80 percent said they had an orgasm.
Question: Several large studies, both here and abroad, have established a clear association in adults between inadequate sleep and obesity. The less we sleep at night on average, the more overweight we are likely to be. Does this same relationship hold for children? A number of small studies have hinted that this is likely to be the case, but, to date, the research has been flawed.
New study: Now comes a carefully done study by Dr. Julia Lumeng of the University of Michigan and her colleagues. The data were drawn from a large National Institute of Child Health and Human Development study, beginning in 1991, that includes more than 1,000 children in 10 areas of the United States, urban and rural. The children were tracked from birth through sixth grade. The children's height and weight were measured when they were in third grade and again when they were in sixth grade. Demographic data on race, socioeconomic status, and gender were also collected because these factors are also known to be associated with the prevalence of obesity, and it was important to separate out those effects from the consequences of inadequate sleep.
Findings: Dr. Lumeng and her colleagues found a clear association in sixth graders between less sleep and more weight: For every additional hour of sleep at night, there was 20 percent less likelihood that the child would be overweight. Shorter sleep duration in third grade increased the likelihood of heaviness in sixth grade. This relationship was even more striking for children when they were measured in third grade—even those who were not then overweight. Every additional hour of nightly sleep in third grade meant a 40 percent lower chance of being overweight three years later. The critical dimension for length of sleep was bedtime. The average awakening time was exactly the same across children's weights, but the average bedtime was later for the chunky kids.
Explanations: Why should this be? There are many proposed answers, none of them definitive. Maybe less sleep makes kids irritable, and then they eat excess food to distract them from expressing their bad mood. Perhaps the relationship is biological: More of the hormone leptin, which decreases appetite, is released when people sleep, and we know that adults produce less of it when they sleep less. Or maybe the key is exercise. In general, longer sleep is associated with higher activity level (though in adult studies the increased physical activity associated with longer sleep didn't seem to be the factor that decreased the risk of obesity).
Conclusion: If, ultimately, it can be demonstrated that inadequate sleep actually causes excess weight gain, how can we help everyone get more sleep? What role do huge homework assignments play in late bedtimes? Should we rethink the early start times for many schools (even though kids' waking times weren't a factor in this study)? What else?
Problem: It's been known for more than 50 years that air travelers are at risk of developing dangerous blood clots in their veins. This is probably because relative immobility and the pressure of sitting lead to blood stagnation, which promotes blood clotting. When clots form in the deep veins of the pelvis or the legs, the condition is called "deep vein thrombosis." Sometimes these clots are carried to the lungs, where they become lodged, causing a pulmonary embolism—and, in some cases, sudden death. The symptoms of DVT are pain and swelling in the affected area and redness of the limb. People with pulmonary embolus typically have a sudden onset of shortness of breath, rapid breathing, chest pain, and cough. The period of risk may continue for up to eight weeks after landing.
Question: How great a risk do these conditions pose to airline travelers? Which fliers are especially at risk? What can we do to prevent these complications of travel?
New study: In a new large and comprehensive study (PDF), Saskia Kuipers of the Leiden (Netherlands) University Medical Center and her colleagues assembled a database of almost 9,000 subjects on air travel, completed by the employees of eight large companies or international organizations. (Here's the questionnaire—you can see it without a password.) The study group was clearly composed of serious travelers, since it took more than 300,000 flights over about five years, averaging 2.6 long flights per person per year.
Findings: Fifty-five of the travelers developed confirmed DVT or pulmonary embolus after flying, a rate of one in 4,650 flights, which is about triple the expected risk. Women had a higher risk than men, and it was magnified (to one in 1,800 flights) by the use of birth control pills. Being of medium height lowered the risk. Being tall increased it, and so did being short (less than 5 feet 5 inches), probably because airline seats put pressure on the back of the legs of people whose feet don't touch the floor. I would not be surprised if the risk were greater for people who were more tightly packed into the cheaper airline seats (and, in fact, the condition is sometimes called "economy-class syndrome"). Kuipers didn't address this factor or discuss whether the companies and organizations she studied bought business- or first-class tickets for employees, which might lead her calculations to underestimate the risk for the rest of us.
Prevention: In general, physical activity diminishes the risk of clotting. Another earlier study suggested that elastic stockings (which keep constant pressure on the lower extremities and prevent blood from stagnating in the veins) might help. People with a history of DVT or pulmonary embolus planning a long trip would do well to speak to their doctor about other precautions.
Conclusion: Actually, I found this study quite reassuring. The risk of these complications is less than I thought it would be. For almost all of us, it certainly doesn't outweigh the benefit of a nice vacation in a far-away place.
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